Cyberjournalist boils down the tips from an ACES session on online hed writing.
• be specific enough to hook readers
• have key words that refer to past stories in the news that are on people's minds during watercooler chat
• be written in a conversational tone
• be simple and straightforward
• give the pertinent information since online hedlines don't typically follow newspaper design strategies such as drop heds
• find a blend of sensationalism and exaggeration
• use "magic" words that everyone is curious about (e.g., babies, spam, the Web, viruses, taxes, reality TV)
Most of these apply to headline writing offline, too. And although the "sensationalism and exaggeration" advice seems like sacrilege, I'd describe it as going just a little over the top. I haven't tooted Slate's horn lately, so ...
Compare their front-page heds with the heds on the actual article:
Front page: Her Freudian Slip Is Showing (with pic of Condi Rice)
These heads seem appropriate for Slate. Is that because it's online? I don't think so; they'd work just as well in a print magazine. But the tone online tends to be lighter, even in the Web portals for print newspapers.